Hornung, J.J, Mulder, E.W.A., Nyhuis, C.J. & Sachs, S. (2024) A new species of Stoilodon (Chondrichthyes: Holocephali) from the Lower Cretaceous of Germany, representing the first record of this chimaeroid genus from Western Europe. Geologie und Paläontologie in Westfalen (2024): 25-41.
—The enigmatic chimaeroid genus Stoilodon Nessov & Averianov, 1996 had been previously known only by mandibular dental plates found in the Upper Jurassic to Lower Cretaceous of the Russian Platform. Here we report the first occurrence of the genus from Western Europe. The new material derives from brackish deposits of the uppermost Berriasian Isterberg Formation of Gronau in Westfalen, northwestern Germany. It comprises two mandibular dental plates, and, for the first time, a fragment of a vomerine dental plate, thus the most comprehensive record currently known for the genus. Furthermore the new material is distinct from previously described specimens and represents a novel species, Stoilodon lindenbergi n. sp.. We restrict the type and only other formally named species, S. aenigma Nessov & Averianov, 1996, to the type region and stratum (Albian-Cenomanian). Other Tithonian and Berriasian occurrences found in the Russian Federation are tentatively referred to as Stoilodon sp. but they may represent distinct species as well. The new material from Germany shows some similarities in the arrangement of dental hypermineralized tissues (especially incipient hypermineralized rods and ovoids in the vomerine dental plate) with crown-group Chimaeroidea. An almost complete reduction of tritors on the oral surface, and oral longitudinal “folds” on the mandibular tooth plates are likewise indicative for derived traits. However, an extensive sheet-like pleromin body in all known dental plates appears to be a plesiomorphic condition. We consider Stoilodon to be a derived taxon relative to more basal “edaphodontids”, and think that a potential placement near the base of crown-group Chimaeroidea is most plausible. However, an unequivocal assignment to an extant family cannot be undertaken, and Stoilodon may represent part of an early stem-group radiation, occupying a peculiar trophic niche. Its occurrence in brackish deposits is palaeoecologically remarkable for being a rare exception among the generally stenohaline chimaeras.
